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760 Occasional Bogging on Full Throttle or High RPM

jwernerny

New member
Joined
Aug 20, 2005
Location
Fairport, NY
So I found myself an $900 '88 760 GLE V6 for a winter/daily driver so I don't have to expose the WRX to another winter. The car is incredibly solid (southern car), and the PO did a lot of work on it to get it in good condition. It also has the B280 motor which solved the cam/oil problem of the B28.

There is one nagging problem he warned me about, occasionally the car bogs (looses power) under full throttle. The engine does not want to rev over 2500 grand or so. The problem can be cured by turning the car off, then back to II without starting for a couple of minutes before starting. Once the car is happy, it doesn't bog anymore, even when continuously driven hard for over an hour. It also revs freely under load up to redline.

It's the intermittent nature of the problem that has me stumped.

Here's what I know/have done so far:
- Gas tank level does not seem to be an issue. It behaves the same with a full or nearly empty tank.
- I've run two cans of Seafoam through the gas tank (two fill-ups).
- I've had the under car fuel filter changed. (I don't play with gas lines that could dump a tank of fuel on me. :-) )

My thoughts (please correct is bad)
- The fact that fuel level doesn't cause a problem means the intake fuel pump is probably okay.
- If the undercar (main) pump was bad, it would not be intermittent.
- The fuel pump relay for the main pump may be temperamental and need replacing.
- The fuel pressure regulator may need replacing.
- There is an intermittent power connection to the main fuel pump.

Any thoughts before I just start throwing money at it?

Thanks
-John
 
I don't know anything about this particular motor family but I would prob start by checking your fuel pressure and FPR before you throw money at it...
 
A factory trained trained Volvo mechanic friend of mine suggested the car is going into limp-home-mode, probably because of a bad MAF (intermittent connection?). I'm going to unplug the MAF tonight and see if I can create the problem at will.
 
After driving the car in it's happy mode, I unplugged the MAF to force the car into limp home mode. It ran much worse than ever: hunted for idle, basically refused all throttle input. Plugged the MAF back in and it was back to running fine.

Looks like things are point back to the fuel system.
 
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